Contents

Configuring DDR·· 1

Overview· 1

Interfaces in DDR· 1

DDR implementations· 1

DDR types· 3

DDR configuration task lists· 3

Packet-triggered DDR configuration task list 3

Auto-dial DDR configuration task list 4

Associating a dial rule with a dialup interface· 4

Configuring bundle DDR· 4

Configuring attributes for a dialup interface· 5

Configuring auto-dial 6

Disconnecting a dialup link· 6

Displaying and maintaining DDR· 6

Troubleshooting· 7

Failure to establish a dialup connection· 7

Ping failure· 7

 

Configuring DDR

DDR in this document is applicable to only PPPoE clients.

Overview

As shown in Figure 1, routers use dial-on-demand routing (DDR) for the following purposes:

·     Setting up a dialup connection over PSTN/ISDN when communication needs arise.

·     Tearing down the connection when the communication is complete.

Figure 1 DDR communication process

 

Ethernet can use DDR to implement access control. For more information, see "Configuring PPPoE."

Interfaces in DDR

DDR uses the following dialup interfaces:

·     Physical interfaces—Include the following interfaces:

?     AM interfaces.

?     AUX interfaces.

?     ISDN BRI interfaces.

?     ISDN PRI interfaces.

?     Cellular interfaces.

·     Dialer interfaces—Logical interfaces used for DDR parameter configurations.

Only dialer interfaces are used throughout this document.

DDR implementations

DDR includes traditional DDR and bundle DDR. The device supports only bundle DDR in the current software version.

Traditional DDR

You can configure traditional DDR by using the following methods:

·     Configure DDR parameters directly on a physical interface.

The router places or receives calls through the physical interface.

The physical interface can have one or more call destinations.

This method applies when only one interface places or receives calls.

·     Configure DDR parameters on a dialer interface.

A dialer interface is associated with a group of physical interfaces and selects a physical interface to place or receive calls.

A dialer interface can have one or more call destinations. A dialer interface with multiple call destinations can use any associated physical interface to place calls to any of the call destinations.

A physical interface can belong to only one dialer interface.

This method applies when one or more interfaces place or receive calls.

Bundle DDR

When using bundle DDR, you can configure DDR parameters only on a dialer interface.

A dialer interface corresponds to a dialer bundle. A dialer bundle can contain multiple physical interfaces. You can assign a priority to each physical interface in the dialer bundle. Each time a call is placed, the highest-priority physical interface available is selected. If multiple physical interfaces with the highest priority are available, these interfaces are selected in a round-robin manner.

A dialer interface can have only one call destination.

A physical interface can belong to multiple dialer bundles and can be used by multiple dialer interfaces at different times.

Comparison of traditional DDR and bundle DDR

Traditional DDR is based on one-to-one bindings between dial services and physical interfaces. A new dial service requires a new physical interface. As a result, traditional DDR has poor extensibility.

 

	NOTE: A dial rule (configured by using the dialer-group rule command) defines one dial service.

 

Figure 2 Relationships among physical interfaces, dialer interfaces, and call destinations in traditional DDR

 

Bundle DDR is simpler and more flexible than traditional DDR. Bundle DDR separates physical interface configuration and logical configuration for calls and allows one-to-many bindings between dial services and physical interfaces. A physical interface can serve multiple dial services.

Figure 3 Relationships among physical interfaces, dialer interfaces, and call destinations in bundle DDR

 

DDR types

Depending on how DDR calls are triggered, DDR includes packet-triggered DDR and auto-dial DDR.

Packet-triggered DDR

You can define packets on a dialup interface as interesting and uninteresting by configuring access control rules. Only interesting packets trigger outgoing calls and reset the link idle-timeout timer.

Before a dialup connection is established, uninteresting packets will be dropped. After a dialup connection is established, uninteresting packets can be forwarded. When the link idle-timeout timer expires, DDR disconnects the connection.

For more information about interesting and uninteresting packets, see "Associating a dial rule with a dialup interface."

Auto-dial DDR

DDR automatically initiates a dialup connection to the remote end upon router startup without requiring a triggering packet. If the connection cannot be established, it will retry at the auto-dial interval. The established connection will not disconnect due to the idle-timeout timer expiration.

DDR configuration task lists

Packet-triggered DDR configuration task list

Tasks at a glance
(Required.) Associating a dial rule with a dialup interface
(Required.) Configuring bundle DDR
(Required.) Configuring attributes for a dialup interface
(Optional.) Disconnecting a dialup link

 

Auto-dial DDR configuration task list

Tasks at a glance
(Required.) Configuring bundle DDR
(Required.) Configuring attributes for a dialup interface
(Required.) Configuring auto-dial
(Optional.) Disconnecting a dialup link

 

Associating a dial rule with a dialup interface

A dial rule determines when a dialup interface initiates DDR calls. You need to configure dial rules only on the initiator of DDR calls.

You can configure a dial rule to match only IP packets or use an ACL to match packets.

Permitted protocol packets or packets that match a permit statement of an ACL are interesting packets. When receiving an interesting packet, DDR performs one of the following operations:

·     Sends it out and resets the idle-timeout timer if a link is present.

·     Initiates a new call to establish a link if no link is present.

Denied protocol packets or packets that match a deny statement of an ACL are uninteresting packets. When receiving an uninteresting packet, DDR performs one of the following operations:

·     Sends it out without resetting the idle-timeout timer if a link is present.

·     Drops it if no link is present.

For DDR to forward packets correctly, configure a dial rule and associate it with the dialup interface.

To associate a dial rule with a dialup interface:

 

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Create a dialer group and configure a dial rule.	dialer-group group-number rule { ip | ipv6 } { deny | permit | acl { acl-number | name acl-name } }	By default, no dialer group is created.
3.     Enter dialup interface view.	interface dialer number	N/A
4.     Associate the dialer group with the dialup interface.	dialer-group group-number	By default, a dialup interface is not associated with a dialer group. A dialup interface can be associated with only one dialer group.

 

Configuring bundle DDR

To configure a dialer interface to place calls, enable DDR.

At the initiator end, the system selects a dialer interface according to the dialer-group rule command configuration.

The initiator end can optionally authenticate the receiving end. To authenticate the receiving end, configure PAP or CHAP authentication on the dialer interface.

To configure bundle DDR:

 

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Create a dialer interface and enter its view.	interface dialer number	N/A
3.     Enable bundle DDR on the interface.	dialer bundle enable	By default, bundle DDR is disabled.

 

Configuring attributes for a dialup interface

Use the following attributes when configuring a dialup interface to improve dial efficiency.

·     Link idle-timeout timer—Starts upon establishment of a link. When the timer expires, DDR disconnects the link.

·     Holddown timer—Starts upon disconnection of a link. The call attempt to bring up this link can be made only after the timer expires. This timer prevents a remote stored program controlled switch (SPCS) from being overloaded.

·     Compete-idle timer—Starts if all physical interfaces are unavailable when DDR initiates a new call. When the amount of idle time of a link reaches the compete-idle timer setting, the link disconnects.

·     Wait-carrier timer—Limits the amount of time DDR waits for a connection to be established for a call. A wait-carrier timer starts when a call is placed. If the connection is not established before the timer expires, DDR terminates the call.

·     Buffer queue length—Length of a buffer queue. With a buffer queue, the dialup interface buffers the packet until a connection is available for packet sending. If no connection is available when a dialup interface without a buffer queue receives a packet, the dialup interface drops the packet.

To configure attributes for a dialup interface:

 

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Enter dialup interface view.	interface dialer number	N/A
3.     Set the link idle-timeout timer.	dialer timer idle idle [ in | in-out ]	By default, the timer is 120 seconds, and only outgoing interesting packets reset this timer.
4.     Set the holddown timer.	dialer timer enable interval	The default setting is 5 seconds.
5.     Set the wait-carrier timer.	dialer timer wait-carrier wait-carrier	The default setting is 60 seconds.
6.     Set the buffer queue length.	dialer queue-length packets	By default, packets are not buffered.
7.     Set a description.	description text	The default setting is in the format of interface-name Interface, for example, Dialer1 Interface.
8.     Set the keepalive interval.	timer-hold seconds	The default setting is 10 seconds.
9.     Set the keepalive retry limit.	timer-hold retry retries	The default setting is five. A link is removed after the keepalive retry limit is reached.
10.     Set the MTU.	mtu size	The default setting is 1500 bytes.
11.     Set the expected bandwidth.	bandwidth bandwidth-value	By default, the expected bandwidth (in kbps) is the interface baud rate divided by 1000.
12.     (Optional.) Specify a primary traffic processing slot for the interface.	·     In standalone mode: service slot slot-number ·     In IRF mode: service chassis chassis-number slot slot-number	By default, no primary traffic processing slot is specified for an interface.
13.     (Optional.) Specify a backup traffic processing slot for the interface.	·     In standalone mode: service standby slot slot-number ·     In IRF mode: service standby chassis chassis-number slot slot-number	By default, no backup traffic processing slot is specified for an interface.
14.     Restore the default settings.	default	N/A
15.     Bring up the dialup interface.	undo shutdown	By default, a dialup interface is up.

 

Configuring auto-dial

With auto-dial enabled, DDR automatically dials a connection to the remote end upon router startup without requiring a triggering packet. If the connection cannot be established, it will retry at the auto-dial interval. The established connection does not disconnect due to the idle-timeout timer expiration as it would in packet-triggered DDR.

To configure auto-dial:

 

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Enter dialup interface view.	interface dialer number	N/A
3.     Set the auto-dial interval.	dialer timer autodial autodial-interval	The default setting is 300 seconds.

 

Disconnecting a dialup link

Execute the dialer disconnect command in any view to disconnect a dialup link.

 

Step	Command
1.     Disconnect a dialup link.	dialer disconnect [ interface interface-type interface-number ]

 

Displaying and maintaining DDR

Execute display commands in any view and reset commands in user view.

 

Task	Command
Display DDR information for a specified dialup interface or all dialup interfaces.	display dialer [ interface interface-type interface-number ]
Display information about dialer interfaces.	display interface [ dialer [ interface-number ] ] [ brief [ description | down ] ]
Clear the statistics on a dialer interface.	reset counters interface [ dialer [ interface-number ] ]

 

Troubleshooting

Failure to establish a dialup connection

Symptom

DDR dialup connection cannot be established because the modem does not dial when the router forwards data.

Solution

To resolve the problem:

1.     Verify that the modem and phone cable connections are correct, and that the modem initialization process is correct.

2.     Verify that DDR is enabled on the dialup interface.

Ping failure

Symptom

The remote end cannot be pinged after the modem is connected.

Solution

To resolve the problem:

1.     Use the debugging ppp all command to verify that the two ends use the same link layer encapsulation and have correct PPP parameters configured for authentication.

2.     Verify that a correct IP address is assigned to the dialup interface.

3.     Verify that DDR is enabled on the dialup interface.

4.     Verify that the correct dialer-group and dialer-group rule commands are configured and associated to ensure that the packets can pass.

5.     Use the debugging dialer event and debugging dialer packet commands to locate the problem.